The 8090 is measured at 44”L X 44”W X 50” H and the 8091 is measured at 44”L X 44”W X 40”H. The 8090 has a removable top which allows for easy loading and cleaning while the 8091 has a non-removable or closed top with a “manway” round entry access cap with a diameter of about 16”. The purpose of the closed top design for the 8091 is to prevent moisture absorption. Another feature to note for the 8090 is that the diameter of the discharge is 10” while the diameter of the discharge for the 8091 is 6”. Please be aware of these distinguishing features as you consider these 2 models.